MXPA99005883A - Composite materials for membrane reactors - Google Patents

Abstract

The present invention relates to composite materials for membrane reactors which include a gas-tight ceramic (28), a porous support (15, 16), and an interfacial zone therebetween. More particularly, this invention relates to composite materials using oxygen ion-conducting dense ceramic membranes (28) formed on a porous support (15, 16) comprising a metallic alloy to provide an interfacial zone identifiable by a gradient of composition in at least one metallic element across the interfacial zone between the dense ceramic membrane and the porous support. Processes using composite materials in accordance with the invention are, for example, used for production of synthesis gas comprising carbon monoxide and molecular hydrogen which synthesis gas is, advantageously, free of deleterious and/or inert gaseous diluents such as nitrogen.

Description

£ COMPOSITE MATERIALS FOR MEMBRANE REACTORS £ Field of Invention The present invention relates to composite materials for membrane reactors which include a * »1 X gas-impermeable ceramic, a porous support, and a . { -x interfacial area between them. More particularly, this invention relates to composite materials using dense ion-conducting ceramic membranes. ** "** •, oxygen formed in a porous support comprising an aluminum alloy to provide an area Interfacial chemical interaction between dense ceramic membrane and porous support. Typically, the Chemical Analysis is identified by a gradient of -r composition in at least one metallic element through -s, you of the iijterfacial zone between the ceramic membrane The dense and porous support, preferably, the chemical interactions equal the coefficient of thermal expansion and other physical properties between the two different materials.

Processes using composite materials according to the invention include converting methane gas into value-added products, for example, 4 * Ref .: 30418 rf "production of synthesis gas comprising carbon monoxide and molecular hydrogen this synthesis gas is advantageously free from deleterious and / or inert gas diluents such as nitrogen.

V Background of the Invention The conversion of low molecular weight alkanes, such as methane, to synthetic or chemical fuels has received increasing attention since low molecular weight alkanes are generally available from reliable and reliable sources. For example, natural gas wells and crude oil wells currently produce large quantities of methane, and low molecular weight alkanes are generally present in coal deposits and could be formed during mining operations, in oil processes, and in the gasification or liquefaction of coal, tar sands, bituminous sand, and biomass.

Many of these alkane sources are located in relatively remote areas, distant from potential users. Accessibility is a major obstacle to the effective and extensive use of remotely located methane, ethane and natural gas. The costs associated with * The liquefaction of natural gas by compression or, alternatively, construction and maintenance of lines to transport natural gas to users are normally prohibitive. Accordingly, methods are desired to convert low molecular weight alkanes to more easily transportable liquid fuels X and chemical feeds and a number of such methods have been reported.

The reported methods can be categorized + ^ < . "*** • Conveniently as direct oxidation routes and / or indirect singles routes.The direct oxidative routes convert lower alkanes to products such as methanol, gasoline, and relatively high molecular weight alkanes.In contrast, indirect singles routes. typically involve the production of synthesis gas as an intermediary. define, or ^ saturated hydrocarbons (paraffins) according to the well-known Fischer-Tropsch process, and by other means. The synthesis gas is not a product; rather, it is typically generated at the site by additional processing. In a few places, synthesis gas is generated by a supplier and sold ** "^" * "out of limit" * for additional processing to value-added products. A potential use for the synthesis gas is as a feed for conversion to high molecular weight paraffins (e.g. aviürfeá "of high quality and high cetane value diesel fuel blending components.The potential application of synthesis gas is for convssion to * large scale ethanol.

To produce high molecular weight paraffins from Preference to * the linear parafams of lower molecular weight (eg C8 to C12), or to synthesize methanol, it is desirable to utilize a synthesis gas feed i. t * which has a H2: CO molar ratio of about 2.1: 1, 1.9: 1, or less. As is well known in art, , s' -r singas conversion reactions by the Fischer-Tropsch method using syngas having relatively high Ha: CO ratios produce hydrocarbon products with relatively large amounts of methane, and relatively low carbon numbers. For example, with a H2: C0 ratio of about 3, relatively large amounts of C1-C8 linear paraffins are typically produced. These materials are characterized by very low octane value and high Reid vapor pressures, and are highly undesirable to use as gasoline.

Decreasing the molar ratio H2: C0 alters the selectivity of the product by increasing the average number of carbon atoms per product molecule, and decreases the amount of methane and light paraffins produced. Thus, it is desirable for a number of reasons to generate syngas feeds having molar ratios of hydrogen to carbon monoxide of about 2: 1 or less.

The above methods for producing synthesis gas from natural gas (typically referred to as "reforming natural gas") can be classified as (a) those that have steam reforming where the natural gas is reacted at high temperature with steam , (b) those that have partial oxidation in which the methane is partially oxidized with pure oxygen by catalytic or non-catalytic means, and (c) reforming of combined cycles consisting of steps of steam reforming and partial oxidation.

The steam reforming involves the reaction at high temperature of methane and steam on a catalyst to produce carbon monoxide and hydrogen. This process, however, results in the production of syngas that have a high ratio of hydrogen to carbon monoxide, usually 3: 1 in excess.

The partial oxidation of methane with pure oxygen provides a product that has a H2: CO ratio close to 2: 1, but large amounts of carbon dioxide and carbon are coproduced, and pure oxygen is an expensive oxidant. An expensive air separation step is required in combined cycle reforming systems, although such processes result in some capital savings since the size of the steam reforming reactor is reduced compared to a direct steam reforming process.

Although the direct partial oxidation of methane using air as a source of oxygen is an alternative power to the steam reforming process *? * > In the current commercial situation, the requirements downstream of the process can not tolerate nitrogen (it is required to * recycle with cryogenic separations), and it has to be used} or * pure xygery. The cost plus .g (nificant associated with partial oxidation is that of the oxygen plant.

Any new process that could use air as the • oxidizer fed and thus avoid the problems of recycling and cryogenic nitrogen separation of "the product stream will have an A. • * dominant economic impact on the cost of a syngan plant , which will be reflected in savings of r - + capital and separation costs.

In this way, it is desirable to decrease the cost of producing syngas, for example, by reducing the cost of the oxygen plant, including the elimination of the cryogenic air separation plant, while improving "production by minimizing co-production of coal. , carbon dioxide and water, to use ** X better the product of a variety of current downstream applications.

The dense ceramic membranes represent a class of materials that offer potential solutions to the aforementioned problems associated with the conversion of natural gas. Certain ceramic materials exhibit electronic conductivities and . 5 ionic (of particular interest is the conductivity of the ! "oxygen ion." These materials not only transport [... oxygen (which function as selective separators of • ** i oxygen), but they transport electrons from behind the catalytic side of the reactor to the oxygen-reduction interface. As such, external electrodes are not required, and if the directed transport potential is sufficient, the partial oxidation reactions must * be spontaneous. Such a system will operate without the need *; of an externally applied electrical potential. Although there are 15 recent reports of various ceramic materials that could be used as partial oxidation ceramic membranes, few works seem to have focused on problems associated with the stability of the material under reaction conditions of methane conversion. * The European Patent Application 90305684.4, published on November 28, 1990, under Publication Ño ". EP 0 399 * 833 Al in the name of Cable et al., Describes an electrochemical reactor using solid membranes comprising: (1) a multi-phase mixture of an electronically conductive material, (2) an oxygen ion conductive material, and / or (3) a mixed metal oxide of a perovskite structure. The reactors are described in which the oxygen of the oxygen-containing gas is transported through a membrane disc to any gas that consumes oxygen. The flow of gases on each side of the membrane disc in the reactor shell shows that they are symmetrical flows through the disk, substantially radially outward from the center of the disk towards the wall of a cylindrical reactor shell. The gases on each side of the disk flow parallel to, and co-current with, each other.

Materials known as "perovskites" are a class of materials that have a crystal structure identifiable with X-rays based on the structure of the perovskite mineral, CaTi03. In its idealized form, the perovskite structure has a cubic lattice in which a unit cell contains metal ions at the corners of the cell, another metal ion at its center and oxygen ions at the midpoints of each edge of the cube. This cubic network is identified as a structure type AB03 where A and B represent metal ions. In the idealized form of perovskite structures, in general, it is required that the sum of the valences of ions A and ions B be equal to 6, as in the model of the perovskite mineral, CaTi03.

A variety of substitutions of cations A and B can occur. Replacing part of a bivalent cation with a trivalent cation or a pentavalent ion with a tetravalent ion, p. ex. , a doping donor, results in two types of charge compensation, that is, electronic and ionic, depending on the partial pressure of oxygen in equilibrium with the oxides. The compensation of charges in the acceptor doped oxides, p. ex. , replacing a bivalent cation for a trivalent cation is by electronic holes at high oxygen pressures but at low pressures it is by vacant oxygen ions. The vacant ions are the route for oxide ions. Therefore, the oxygen flow can be increased by increasing the amount of substitution of lower valence elements by a higher valence metal ion. The oxygen flow reported in perovskites tends to follow the direction suggested by the load compensation theory. While the primary property of high oxygen flow seems to be feasible in a few combinations of doping agents in the ABÜ3 type oxides, many other questions need to be answered about the ideal material to build a novel membrane reactor. For example, the mechanical properties of the selected membrane must have the strength to maintain integrity under the reaction conditions. It must also maintain chemical stability for long periods of time at reaction conditions. Oxygen flow, chemical stability, and mechanical properties depend on the stereoimeter of the ceramic membrane.

Many materials that have the perovskite type structure (type AB03) have been described in recent publications including a wide variety of multiple cationic substitutions at sites A and B mentioning that they are stable in the perovskite structure. Similarly, a variety of more complex perovskite compounds are reported that contain a mixture of metal ions A and metal ions B (in addition to oxygen). The publications referred to p rovschites include: P. D. Battle et al., J. Solid State Chem./ 76, 334 (1998); Y. Takeda et al., Z. Anorg. 'Állg. Chem., 550 / 541,259 (1986); Y. Teraoka et al., Chem. Lett., 19, 1743 (1985); M. Harder and H. H. Muller-? U ^ schbaum, Z. Anorg. Allg. Chem., 464,169 • - * (1980); C. Greaves et al., Acta Cryst. B31,641 (1975) For example, Hayakawa et al. U.S. Patent No. 5,126,499, incorporated herein by reference, describes a process for the production of hydrocarbons by oxidative coupling of methane using a perovskite type oxide having the following composition: M x. { Co _xFe x 0 where M maintains at least one alkaline earth metal x is a number greater than zero but not greater than one and y is a number in the range of 2.5-3.5 at a temperature of 500 ° to 1000 ° C.

Commonly assigned U.S. Patents Nos. 5,580,497 and 5,639,437 in the names of Uthamaligam Balachandran, Mark S. Kleefisch, Thaddeus P. Kobylinski, Sherry L. Morissette and Shiyou Pei, incorporated herein by reference, set forth the preparation, structure and properties of a class of metal oxide compositions. mixed of at least strontium, cobalt, iron and oxygen, and is incorporated herein by reference in its entirety. The use of mixed metal oxides in dense ceramic membranes having electronic conductivity and ionic oxygen conductivity is described as well as their use in the separation of oxygen from a gas mixture containing oxygen to form a first oxygen depleted product and optionally reacting recovered oxygen with organic compounds in another gas mixture.

The ceramic powders with variant stoichiometry are made by reaction in solid state of the constituent carbonates and nitrates. Appropriate amounts of reagents are mixed, in general, and ground in methanol using zirconia medium for several hours. After drying, the mixtures are calcined in air at elevated temperatures, e.g. ex. up to about 850 ° C for several hours, typically, with an intermittent mill. After the final calcination, the powder is milled to a small particle size. The morphology and particle size distribution can play a significant role during the manufacture of membrane tubes.

The membrane tubes can be conveniently manufactured by known methods of plastic extrusion. To prepare for extrusion, the ceramic powder is generally mixed with various organic additives to make a formulation with sufficient plasticity that is easily formed in various forms while maintaining satisfactory strength in the immature state. This formulation, known as an enamel bath, generally consists of a solvent, a dispersant, a binder, a plasticizer, and ceramic powder. The role of each additive is described in Balachandran et al., Internal Proceedings of the Gas Research Conference, Orlando, Florida (H. A. Thompson editor, Government Institutes, Rockville, Md.) Pp. 565-573 (1992). The relationships of various constituents of an enamel bath vary, depending on the formation process and the characteristics of the ceramic powder as particle size and specific surface area. After the enamel bath is prepared, the solvent is allowed to evaporate; this produces a plastic mass that is forced through a die at high pressure (approximately 20 MPa) to produce hollow tubes. The tubes have been extruded with an external diameter of approximately 6.5 mm and lengths of up to approximately 30 cm. The wall thicknesses are in the range of 0.25 to 1.20mm. In the immature state (p. ex. , before heating), the extruded tubes show great flexibility.

The extruded tubes are heated at a slow heating rate (5 ° C / h) in the temperature range of 150 ° to 400 ° C to facilitate the removal of gaseous species formed during the decomposition of organic additives. After the organics are removed at low temperatures, the heating rate increases to about 60 ° C / h and the tubes are sintered at about 1200 ° C for 5 to 10 h. All heating is done in still air. The operating characteristics of the membranes depend on the stoichiometry of the compound. The integrity of the tubes is manufactured using certain ranges of stoichiometry of cations in the ceramic.

In U.S. Pat. No. 5,573,737 commonly assigned to Uthamalingam Balanchadran, Joseph T. Dundek, Mark S. Kleefisch and Thaddeus P. Kobylinski a functionally gradient material is described as including an external tube of perovskite, which makes contact with air; a zirconium oxide inlet pipe that makes contact with the methane gas, and a boundary layer between the perovskite and zirconium oxide layers Even though the functionally gradient oxide materials set forth in U.S. Pat. No. 5,573,737 show greater stability than other known compositions, under certain conditions, are certain problems associated with those in the form of unsupported reactor tubes. The reactor tubes may fracture in the regions slightly away from the hot reaction zone where the tube temperatures may, e.g. ex. , fall from approximately 800 ° C to approximately 700 ° C in the fault regions.

Therefore, it is an object of the present invention to provide stable composite materials for membrane reactors which include a gas impermeable ceramic having a composition that exhibits ionic and electronic conductivity as well as appreciable oxygen permeability.

It is another object of the present invention to provide stable composite materials for membrane reactors useful in converting low value hydrocarbons to high value products. These compositions show great stability when exposed to a gas reducing environment and other operating conditions for periods of time. prolonged It is an object of the invention to overcome one or more of the problems described above.

Other objects and advantages of the invention will be apparent to those skilled in the art from a review of the following detailed description, taken in conjunction with the drawings and appended claims.

- Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims.

Brief Description of the Invention In a broad aspect, the present invention is directed to composite materials for membrane reactors including a gas impervious ceramic, a porous support, and an interface therebetween. More particularly, this invention relates to composite materials using dense ceramic membranes that conduct the oxygen ion formed in a porous support comprising a metallic alloy to provide an interfacial zone of chemical interaction between the dense ceramic membrane and the porous support. Advantageously such composite materials are used for membrane reactors which convert, for example, natural gas to synthesis gas by controlled partial oxidation and reforming reactions, and when the subsequent conversion of the synthesis gas to value-added products is desired, for example , by a process of water-gas change.

In one aspect, the invention is a composite material for membrane reactors, such a composite material comprising: A dense ceramic membrane comprising a crystalline mixed metal oxide showing, at operating temperatures, electronic conductivity, ionic oxygen conductivity, and ability to separate oxygen from an oxygen-containing gaseous mixture and one or more components by means of the conductivities; A porous support comprising an alloy of at least two metallic elements this support shows mechanical stability at the operating temperature; Y An interfacial zone of chemical interaction between the dense ceramic membrane and the porous support.

Preferably the dense ceramic membrane in the composition is made of a metal oxide mixed in a particulate form by compressing the particulate oxide against the porous support at elevated temperatures, whereby the chemical interactions between the porous alloy and the mixed metal oxide form an area interfacial.

In another aspect, the invention is a hollow tubular module for membrane reactors, this module comprises: A dense ceramic membrane comprising a crystalline mixed metal oxide that exhibits, at operating temperatures, electronic conductivity, ionic ionic conductivity, and ability to separate oxygen from an oxygen-containing gaseous mixture and one or more components by means of the conductivities; An internal porous tube comprising an alloy of at least two metallic elements this tube shows mechanical stability at the operating temperature; A first interface between the dense ceramic membrane and the inner porous tube having, through the interface, a composition gradient in at least one metal element; An external porous tube comprising an alloy of at least two metallic elements this tube shows mechanical stability at the operating temperature; Y A second interface between the dense ceramic membrane and the external porous tube having, through the interface, a gradient of composition in at least one metal element.

Preferably the dense ceramic membrane in the tubular module is made of a metal oxide mixed in a particulate form by compressing the particulate oxide against the internal and external porous tubes at temperatures in a range from about 500 ° C to about 1250 ° C, what the composition gradients that define the first and second interface areas are obtained.

In another aspect, the invention is a process for converting organic components into value-added products, the composite material comprising: Providing a membrane reactor comprising a plurality of the hollow tubular module described hereinbefore; Contacting the external porous tubes of the hollow tubular module with a gaseous mixture containing oxygen having a relatively higher partial pressure of oxygen; Contacting the inner porous tube of the hollow tubular module with a gaseous composition having a relatively lower partial pressure of oxygen; Y; Allowing oxygen to be transported through the dense ceramic membrane by means of its electronic conductivity and ionic oxygen conductivity thus separating the oxygen from the oxygen-containing gas mixture having a relatively higher partial pressure of oxygen in the gas composition which has a relatively lower partial pressure of oxygen.

In preferred embodiments of the invention the crystalline mixed metal oxide composition is selected from a class of materials having an X-ray identifiable crystalline structure based on the structure of the perovskite mineral, CaTi03.

In other preferred embodiments of the invention the crystalline mixed metal oxide composition is selected from a class of materials represented by D a E a + ß O where D comprises at least one metal selected from the group consisting of magnesium, calcium, strontium, and barium, E comprises at least one element selected from the group consisting of vanadium, chromium, magnesium, iron, cobalt, and nickel, OI is a number in a range of about 1 to about 4, ß is a number in a range of about 0.1 to about 20, such that 1. 1 < (a + ß) / a = 6, and d is a number making the neutral charge of the compound, wherein the crystalline mixed metal oxide composition has a crystalline structure comprising layers having a perovskite structure held apart by layers of pigment having different structure identifiable by X-ray powder diffraction pattern analysis means, the composition such that a dense ceramic membrane comprising the composition shows electronic conductivity and ionic oxygen conductivity, and the ability to separate oxygen from a gas mixture containing oxygen and one or more volatile components by means of the conductivities.

The invention also includes the use of composite materials in membrane reactors for the separation of oxygen from a gas mixture containing oxygen. Typically in such processes the aforementioned composite materials are used in separation apparatus for oxygen transfer of a first gas mixture containing oxygen having a relatively higher partial pressure of oxygen to a second gas mixture having a relatively low oxygen partial pressure. lower and preferably containing one or more components, more preferably including organic compounds that react with oxygen. An essential feature of each selectively permeable dense ceramic membrane of composite materials is that it retains its ability to separate oxygen for an adequate period of time under operating conditions.

The present invention also relates to the preparation, structure, and properties of dense ceramic membranes comprising mixed metal oxide compositions that exhibit electronic conductivity and ionic oxygen conductivity, and ability to selectively separate oxygen from a gas mixture that It contains oxygen and one or more volatile components by means of the conductivities.

An essential characteristic of such selectively permeable material is that it retains its ability to separate and transport oxygen for an adequate period of time.

Brief Description of the Drawings The appended claims establish the new features that characterize the present invention. The present invention, as well as advantages thereof, could be better understood, in this way, by reference to the following brief description of the preferred embodiments taken in conjunction with the appended drawings, in which: FIGURE 1 is a longitudinal view, in partial section, showing the apparatus to demonstrate aspects of a hollow tubular module for membrane reactors using composite material comprising dense ceramic leading to the oxygen ion according to the present invention; FIGURE 2 is a perspective view of a sectioned disc of the apparatus set forth in FIGURE 1; FIGURE 3 is a cross-sectional view of the disc shown in FIGURE 2; FIGURE 4 is a digital image, of a scanning electron microscope, showing the position by line scan analysis through regions of mixed metal oxide, porous metal support, and interfacial zone therebetween; Y FIGURE 5 is a graphical presentation of the results of the line scan analysis in the position shown in FIGURE 4.

For a more complete understanding of the present invention, reference should now be made to the embodiments illustrated in greater detail in the appended drawings and described below in the form of examples of the invention.

Description of the invention As stated above, dense ceramic membranes used in accordance with this invention comprise a crystalline mixed metal oxide that exhibits, at operating temperatures, electronic conductivity, ionic ionic conductivity, and ability to separate oxygen from an oxygen-containing gaseous mixture. and one or more volatile components by means of the conductivities.

A preferred class of dense ceramic materials that lead to the oxygen ion in U.S. Pat. Nos.: 5, 580, 497; 5,639,437 and (08 / 625,119) commonly assigned to Balanchandran Kleefisch, Kobylinski, Morissette and Pei, whose patents are specifically incorporated herein by reference in their entirety.

Particularly useful crystalline mixed metal oxide compositions are selected from a class of materials represented by D a E a + ß O where D comprises at least one metal selected from the group consisting of magnesium, calcium, strontium, and barium, E comprises at least one element selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, and nickel, is a number in the range of about 1 to about 4, ß is a number in a range from above 0.1 to about 20, such that 1. 1 < (a + ß) / a = 6, and d is a number representing the neutral charge of the compound.

The dense ceramic membranes used according to this invention advantageously and preferably comprise a crystalline mixed metal oxide having a crystalline structure comprising layers having perovskite structure held apart by bridging layers having a different identifiable structure by means of analysis of powder X-ray diffraction pattern. The composition of such dense ceramic membranes shows electronic conductivity and ionic oxygen conductivity, and ability to separate oxygen from a gas mixture containing oxygen and one or more volatile components by means of the conductivities.

Useful dense ceramic membranes advantageously comprising the crystalline mixed metal oxide composition are represented by (^? (tJfi + ß os where D is a metal selected from the group consisting of magnesium, calcium, strontium and barium, M 'is a metal selected from the group consisting of magnesium, calcium, strontium, barium, copper, zinc, silver, cadmium, gold, and mercury , E is an element selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, and nickel, G is an element selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, niobium, molybdenum, technetium, ruthenium, radium, palladium, indium, tin, antimony, rhenium, lead and bismuth, with the proviso that D, E, G and M 'are different elements, and a number in a range of approximately 0.1 to approximately 0.5, x is a number in a range of about 0.1 to about 0.8, a is a number in the range of about 1 to about 4, β is a number in a range of 0.1 to about 20, preferably β is a number in a range of about 0.1 to approximately 6, such that Ll < (a + ß) / a = 6, and d is a number representing the neutral charge of the compound.

In preferred embodiments of the invention the crystalline mixed metal oxide composition is represented by & < * (Fe? -xc ° x) a + ß where x is a number in a range of 0.01 to about 1, OI is a number in a range of about 1 to about 4, ß is a number in a range of about 0.1 to about 20, such that 1 < (a + ß) / a < 6, and d is a number representing the neutral charge of the compound, and wherein the crystalline mixed metal oxide composition has a crystalline structure comprising having a perovskite structure held apart by bridge layers having a different structure identifiable by means of of powder X-ray diffraction pattern analysis, the composition such that a dense ceramic membrane comprising the composition shows electronic conductivity and ionic oxygen conductivity, and ability to separate oxygen from a gas mixture containing oxygen and one or more volatile components by means of conductivities.

In other preferred aspects of the invention the crystalline mixed metal oxide composition is represented by where M is an element selected from the group consisting of yttrium, barium, and lanthanum, X is a number in a range of about 0.1 to about 0.95, preferably X is a number in a range of 0.1 to 0.8, and Y is a number in a range of about 0.01 to about 0.95, preferably Y is a number in a range above 0.1 to about 0.5, a is a number in a range of about the approximately 4, β is a number in a range of about 0.1 to about 20, preferably β is a number in a range from about 0.1 to about 6, such that 1. 1 < (a + ß) / a = 6, and d is a number which makes the compound charge neutral.

In still other preferred aspects of the invention the composition of the crystalline mixed metal oxide is represented by SrFeCo0 > fifty? wherein d is a number representing the neutral charge of the compound, and wherein the composition has a powder X-ray diffraction pattern comprising substantially significant lines as described in Table I.

Table I Main XRD lines Spacing Effort Assigned Interplanar d, Á1 9. 52 + 0.05 Weak 3. 17 + 0.05 Weak 2. 7710.05 Medium-Strong 2. 7610.05 Medium-Strong 2. 7310.03 Very Strong 2. 0810.03 Weak-Medium 1. 9610.02 Medium 1. 9010.02 Weak-Medium 1. 592 + 0.01 Weak-Medium 1.587 + 0.01 Medium 1. 566 + 0.01 Weak 1 Angstroms As is generally known, the assigned stresses in X-ray diffraction patterns may vary depending on the characteristics of the sample. The stress of the line observed in any particular sample could vary from another sample, for example, depending on the amounts of each crystalline phase, oxygen content and / or amorphous material in a sample. Also, the X-ray diffraction lines of a particular crystalline material could be obscured by lines of other materials present in a measured sample.

The crystalline mixed metal oxide compositions used, too, may be selected from a class of known materials, in general, such as perovskites having an X-ray identifiable crystalline structure based on the structure of the perovskite mineral, CaTi03. In its idealized form the perovskite structure has a cubic lattice in which a unit cell contains metal ions at the corners of the cell, another metal ion at its center and oxygen ions at the midpoints of each edge of the cube. This cubic network is identified as a structure of type AB03 where A and B represent metal ions. In the idealized form, perovskite structures require that the sum of the valences of ions A and B be equal to 6, as in the perovskite mineral model, CaTi03.

Preferred membranes include an inorganic crystalline material comprising strontium, iron, cobalt, and oxygen, preferably having a powder X-ray diffraction pattern comprising substantially significant lines as described in Table I. Advantageously, the mixed metal oxide crystalline demonstrates ionic conductivity of oxygen and electronic conductivity. The invention includes the method of preparation for crystalline mixed metal oxide compositions containing at least strontium, cobalt, iron, and oxygen.

As mentioned above, the mixed metal oxide materials used in the dense ceramic membranes of this invention include any single phase and / or multi-phase, dense phase, intimate mixture of materials having electronic conductivity and ionic oxygen conductivity. In relation to solid metallic oxide materials, the terms "mixture" and "mixtures" include materials comprising two or more solid phases, and materials of a phase in which the atoms of the included elements are mixed in the same phase solid, as in zirconia stabilized with yttria. The term "multiphase" refers to a material that contains two or more interspaced solid phases without forming a one-phase solution. The useful core material therefore includes the multiphase mixture which is "multiphase" because the electronically conductive material and the oxygen ion conducting material are present as at least two solid phases, such that the atoms of the various components of the multi-component solid do not mix with one another mainly, in the same solid phase.

The multi-phase solid core materials are described in European Patent Application Number: 90305684.4, published on November 28, 1990, under Publication No. No. EP 0 399? 33 To the disclosure of which is incorporated herein by reference.

In the indirect method for making a dense ceramic membrane containing a mixed metal oxide material having a crystalline structure according to the invention, a solid oxide is made and exchanged to a powder, the powder is mixed in a plastic mass with the solvent liquid and optionally additives, a desired shape formed from the plastic mass, and the form is heated to temperatures sufficient to form a dense and solid ceramic having electronic conductivity and ionic oxygen conductivity. Typically, such ceramics are obtained at temperatures in a range above about 500 ° C, and generally at temperatures in a range above about 800 ° C.

The porous supports for use according to this invention can be made of some suitable alloy exhibiting mechanical stability at the operating temperature. Particularly alloys are used, such as nickel-based steel alloys. Suitable alloys advantageously and preferably have coefficients of expansion equal to those of the ceramic used, e.g. ex. within a range of approximately 25 percent of the coefficient of expansion of the ceramic, more preferably within approximately 15 percent. Preferred alloys include nickel-iron-chromium alloys having the following limiting chemical composition: Element Percent Element Percent Nickel 30.0-35.0 Silicon 1.0 max.

Iron 39.5 min Copper 0.75 max.

Chrome 19.0-23.0 Aluminum 0.15-0.60 Carbon 0.06-0.10 Titanium 0.15-0.60 Manganese 1.50 max Al + Ti 0.85-1.20 Sulfur 0.015 max Alloys having such a chemical composition are commercially available under the names INCOLY 800 alloy and INCOLY 800HT alloy.

Porous metallic products are made by compaction and sintering (heating), and other well-known methods (See, for example, Kirk-Othmer Encycl opedia of Chemi cal Technolgy, third edition, Vol. 19, pages 28-61, John Wiley & Sons, Inc. 1982). In porous materials, the void space that determines porosity is controlled as the amount, type, and degree of interconnection. When in contact with gases containing oxygen and / or organic compounds for a long period of time at elevated temperature, the appropriate porous supports remain advantageously and preferably rigid, do not change in porosity and are resistant to corrosion reactions such as oxidation and carbonization. . Chromium in the alloy promotes the formation of a protective surface oxide, and nickel provides good retention of the protective coating, especially during cyclic exposure at high temperatures.

The ceramic membrane that conducts the oxygen ion provides a gas-impermeable partition between the external porous tube and the internal porous tube of the hollow tubular module where the ceramic is impenetrable to the components of the gaseous mixture containing oxygen at room temperature. When a gaseous mixture containing oxygen having an appropriately high partial pressure of oxygen, e.g. ex. in a higher range of approximately 0.2 atm., it is applied to a dense ceramic membrane of this type (through the external porous tube), the oxygen will adsorb and dissociate on the surface, become ionized and diffuse through of the ceramic on the other side and it will be deionized, associated and desorbed as the oxygen separates into another gaseous mixture (through the internal porous tube) that has a lower oxygen partial pressure than that applied to the external surface. The electron circuit necessary to supply this ionization / deionization process is advantageously maintained internally in the oxide by its electronic conductivity.

Suitable oxygen-containing gaseous mixtures as the feed streams for the present process typically contain between about 10 mol percent to 50 mol percent oxygen. Water, carbon dioxide, nitrogen and / or other gaseous components are typically present in the feed mixes. A preferred gas mixture containing oxygen is atmospheric air. Volatile hydrocarbons that are converted to carbon dioxide and water under the operating conditions of the process could be included in small quantities without causing adverse effects on the separation process. Representative of such hydrocarbons are linear and branched alkanes, alkenes and alkynes having 1 to about 8 carbon atoms.

A difference in the partial pressure of oxygen between the first and second zone, p. ex. , through the membrane, provides the driving force for the separation of oxygen from a gaseous mixture containing oxygen at process temperatures sufficient to cause oxygen to adsorb in the first zone, become ionized on the first surface and is transported through the ceramic membrane in ionic form to the second surface of the ceramic membrane and the second zone where the partial pressure of oxygen is lower than in the first zone. The transported oxygen is collected and / or reacted in the second zone where the ionic oxygen is converted to the neutral form by the release of electrons on the second surface.

An excess partial pressure of oxygen in the first zone above that of the second zone (positive difference of oxygen partial pressure) can be created by compressing the gas mixture in the first zone at a pressure sufficient to recover transported oxygen, e.g. ex. , a current permeable to oxygen, at a pressure greater than or equal to approximately one atmosphere. Typical feed pressures range from about 15 psia to about 250 psia, depending largely on the amount of oxygen in the feed mixture. Conventional compressors can be used to achieve the compression required to practice the present process.

Alternatively, a positive difference of the partial pressure of oxygen between the first and second zone can be achieved by reaction of the oxygen carried with an oxygen-consuming substance, such as a volatile organic compound, to form oxygen-containing products with added value and / or mechanically evacuating the second zone at a pressure sufficient to recover the oxygen transported. Advantageously, a gaseous mixture containing organic compounds such as methane, ethane, and other light hydrocarbon gases, for example natural gas under well head pressures of several hundred psi, is fed into the second zone where at least one of the compounds reacts with the oxygen transferred in the zone to form oxidation products with added value.

Oxygen-containing gas vapors flowing through the first surface of the dense ceramic membranes in the gas separation apparatus of this invention can be air, pure oxygen, or any other gas containing at least about 1 percent oxygen free mol. In another embodiment, the gas stream containing oxygen contains oxygen in other forms such as N20, NO, S02, S03, (H20) vapor, C02, etc. Preferably, the oxygen-containing gas vapor contains at least about 1 mole percent of free molecular oxygen (dioxygen) and more preferably the vapor of the oxygen-containing gas is air.

As mentioned above, the processes according to the present invention include processes for the preparation of synthesis gas by the reaction of a gas stream containing oxygen with a hydrocarbyl compound in another gas stream without contaminating the hydrocarbyl compound and / or the products of oxidation with other gases of the gas stream containing oxygen, such as nitrogen from an air stream. Syngas, a mixture of carbon monoxide (CO) and molecular hydrogen (H2), is a valuable industrial feed for the manufacture of a variety of useful chemicals *. For example, the synthesis gas can be used to prepare methanol or acetic acid. The synthesis gas can also be used to prepare high molecular weight alcohols or aldehydes as well as higher molecular weight hydrocarbons. The synthesis gas produced by the partial oxidation of methane, for example, is an exothermic reaction and produces the synthesis gas having a used ratio of hydrogen to carbon monoxide, according to the following equation: CH4 + 1/20,? 2HP + CO Preferred embodiments include the processes for preparing the synthesis gas by partial oxidation of any vaporizable hydrocarbyl compound. The hydrocarbyl compound used in the processes of this invention appropriately comprise one or more gaseous or vaporizable compounds that can be reacted with molecular oxygen or carbon dioxide to form the synthesis gas. More suitably, the hydrocarbyl compound is a hydrocarbon such as methane and / or ethane, however, various amounts of oxygen or other atoms may also be in the hydrocarbyl molecule. For example, hydrocarbyl compounds that can be converted to synthesis gas include methanol, dimethyl ether, ethylene oxide, and the like. However, the most preferred hydrocarbyl compounds are low molecular weight hydrocarbons containing about 1 to about 20 carbons, more preferably 1 to about 10 carbon atoms. Methane, natural gas, which is mainly methane, or other mixtures of light hydrocarbons that are readily available, cheap, particularly hydrocarbyl feedstocks are preferred for processes of this invention. Natural gas can be natural gas from the head of the well or natural gas processed. The composition of the processed natural gas varies with the needs of the last user. A typical processed natural gas composition contains, on a sega or water-free basis, about 70 weight percent methane, about 10 weight percent ethane, 10 percent at 15 percent C02, and the balance It is made of smaller amounts of propane, butane and nitrogen. Preferred hydrocarbyl feedstocks also contain water at levels of about 15 percent these levels are useful in mitigating the heat of any oxidation reaction. Mixtures of hydrocarbyl compounds and / or hydrocarbons can also be used.

Preferred Modalities of the Invention FIGURE 1 illustrates the apparatus for demonstrating aspects of the hollow tubular module for membrane reactors using composite material comprising dense ceramic conducting the oxygen ion according to the present invention. As set out in the partial section view 11, a device according to this invention comprises a support base 14 to which an internal porous metal tube 15 and an external porous metallic tube 16 are attached, advantageously, by welding them. The porous metal tubes are sized and arranged to provide an annular cavity for forming and supporting a gas impervious ceramic 28 comprising a crystalline mixed metal oxide composition. The device is provided with a cylindrical die 18 which is dimensioned closely to the annular cavity 28, bolt 12, nut 22, washer 24 and spring 26. During the formation of composite materials of the invention at elevated temperatures, the force is applied to particulate precursors of any ceramic desired by the spring 26 which is advantageously in a region of low temperature.

Other suitable methods for forming the impervious to the supported gas ceramic include melting particulate ceramics from ceramic sources at elevated temperature, for example about 1200 ° C, CVD, Plasma, atomizer, etc.

Suitable porous metallic materials should have thermal expansion coefficients not so different from those of the ceramic at operating temperatures, preferably within about 10 percent of the coefficient of thermal expansion of the ceramic. Useful porous metallic materials typically comprise an alloy of at least two metal elements this alloy shows mechanical strength at the operating temperature.

In a cross-sectional view perpendicular to the section of FIGURE 1 the gas impervious ceramic can have any closed geometry shape, which is preferably selected from circular, square or rectangular, and, more preferably, circular. The preferred hollow tubular module for membrane reactors of this invention comprises dense ceramic membrane and porous metal tubes forming concentric cylinders.

While a present embodiment of the invention has been described, it will be distinctly understood that the invention is not limited thereto, but could be modeled and practiced otherwise within the scope of the following claims.

Examples of the Invention The following Examples will serve to illustrate certain specific embodiments of the invention set forth herein. These Examples should not be constructed, however, as limiting the scope of the new invention since there are many variations that could be made therein without deviating from the spirit of the disclosed invention, as will be recognized by the skilled artisan.

Example 1 This example demonstrates the preparation of a hollow tubular module using the apparatus set forth in the porous tubes of FIGURE 1 of 316 stainless steel alloy having external diameters (OD) of "and W and 5 μm pore size.

The annular cavity between the coaxially placed tubes (approximately 3"long) was charged with particulate precursors of a desired ceramic comprising a fine agglomerate with which it has stoichiometry Sr Fe Co0.5 Os but is not yet formed in a single crystalline phase. This agglomerate was purchased by specification from Praxair Specialty Ceramics, Seattle, Wash. The entire apparatus was placed in a nearby alumina tube (1"OD) which was evacuated by means of a vacuum pump. The alumina tube containing the apparatus was inserted into an oven that was heated at a rate of 5 ° C per minute up to 1000 ° C, holding at 1000 ° C for 2 days and cooled at a rate of 5 ° C per minute under vacuum. A diamond saw was used to cross section the resulting composite into thin discs for analysis.

FIGURE 2 is a perspective view of a sectioned disc of the apparatus. A first interface was formed between the inner porous tube 15 and the ceramic 28 which had, through the interface, a composition gradient. In the same way a second interface was formed between the ceramic 28 and the external porous tube 16.

The chemistry through these interfacial zones was studied by electronic microcopy. One of the discs was immersed in methylmethacrylate resin. A polished cross section was prepared using standard metallographic techniques and the polished cross section was carbon coated by vacuum evaporation. A scanning electron microscope (SEM) was handled in the form of electronic image formation of return diffusion (BSEI), which shows, mainly, the compositional contrast (the compositions of higher atomic number are brighter). X-ray spectrometry analysis of energy dispersants (EDXS) was done in the SEM with the electronic probe that sweeps a field, identified by "F", a partial field, identified by "PF", or a stationary probe on a point, identified by "S". The SEM / EDXS analysis can detect all boron and heavier elements. The evaporated carbon coating makes a minor contribution to the C signals in the spectrum. Elemental distributions through the stainless steel / ceramic interface were determined by obtaining the line scan profiles for O, Sr, Cr, Fe, Co, and Ni.

Figure 4 is a digital image, of a scanning electron microscope, showing the position by line scan analysis through the regions of mixed metal oxide, porous metal support, and interfacial zone therebetween. The ceramic is on the left side and the porous steel is on the right side.

The interface, which is approximately 10 μm thick, appears to be two layers - the brighter layer of BSEI (ceramic side) seems to have a uniform, dense composition, and the darker layer of BSEI (side of steel) seems porous and more complex. The line scan covers approximately 15 μm (see FIGURE 5 which is a graphical presentation of the results of the line scan analysis in the position shown in FIGURE 4). The BSEI digital image has a horizontal line that shows the location of the line scan (100 analysis points from one endpoint to the other), and the cross fiber marker in each line scan corresponds to the position of the vertical line in each elementary profile of corresponding line scan. As shown, the cross fiber is at the boundary between the interface and the stainless steel.

The line scan extends from one ceramic region to the left through an interfacial zone (approximately 5 μm), and to the right, steel with two pores (approximately 5 μm and approximately 15 μm from the cross fiber marker). The distance of 5 μm is close enough to the ceramic that the pore surface is covered with a Sr-Cr-O species, while the more distant pore (15 μm) shows a Sr-O species. The steel regions have characteristics of the alloy with the increase in the concentration of Ni in the interface. The concentration of Ni falls because the Sr-Cr oxide is embedded in the surface of the pores. The interface is predominantly a Cr-Fe-0 system with higher Cr on the right side of the interface. An inverse relationship between Cr and Fe appears in the region.

Some observations which can be made from the results of the line scan are as follows: (1) the ceramic appears to have a clearly uniform Sr-Fe-Co-Ba-0 composition, except that the Co level appears to vary significantly; (2) the steel has a uniform composition of Fe-Cr-Ni-Mo, except that the levels of Mo and Ni increase in the last pair of micrometers up to the limit of the interfacial zone; (3) the ceramic side of the interfacial zone is rich in O, Fe, and Co, while the stainless steel side of the interfacial zone is rich in O and Cr and some Mo; (4) there seems to be very little Sr in the interfacial zone, but something is observed in the pores within the stainless steel layer; (5) Although part of the carbon signal is from the evaporated carbon coating, there seems to be slightly more carbon in the ceramic than in the stainless steel, and even more carbon in the interfacial zone.

For the purposes of the present invention, "predominantly" is defined as more than about 50 percent. "Substantially" is defined as occurring with sufficient frequency or occurring in such proportions as to measurably affect the macroscopic properties of an associated component or system. Where the frequency or proportion for such an impact is not substantially clear is considered to be approximately 20 percent or more. The term "Essentially" is defined as absolutely except that small variations are permitted which have no more than a negligible effect on macroscopic qualities and final consequences, typically up to about one percent.

The examples and advanced hypotheses have been presented here to better communicate certain facets of the invention. The scope of the invention is determined solely by the scope of the appended claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (10)

1. A composite material for membrane reactors, characterized in that the composite material comprises: (a) a dense ceramic membrane comprising a crystalline mixed metal oxide showing, at operating temperatures, electronic conductivity, ionic ionic conductivity, and ability to separate oxygen from a gas mixture containing oxygen and one or more components by of conductivities; (b-1) a porous support comprising an alloy of at least two metallic elements this support shows mechanical stability at the operating temperature; Y (c-1) an interfacial zone of chemical interaction between the dense ceramic membrane and the porous support.

2. The composite material according to claim 1, characterized in that the dense ceramic membrane is made of metal oxide mixed in a particulate form by compressing the particulate oxide against the porous support at elevated temperatures, whereby the chemical interaction defining the zone is obtained interfacial.

3. The composite material according to claim 1, characterized in that the composition of the crystalline mixed metal oxide is selected from a class of materials having a crystal structure identifiable with X-rays based on the structure of the perovskite mineral, CaTi034. The composite material according to claim 1, characterized in that the crystalline mixed metal oxide composition is represented by

D a E a + ß O where D comprises at least one metal selected from the group consisting of magnesium, calcium, strontium, and barium, E comprises at least one element selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, and nickel, a is a number in the range of about 1 to about 4, ß is a number in a range of about 0.1 to about 20, such that 1. 1 < (a + ß) / a = 6, and d is a number representing the neutral charge of the compound, wherein the crystalline mixed metal oxide composition has a crystalline structure comprising layers having perovskite structure held apart by bridging layers having a different structure identifiable by means of analysis of powder X-ray diffraction pattern, the composition such that a dense ceramic membrane comprising the composition shows electronic conductivity, ionic ionic conductivity, and ability to separate oxygen from a gas mixture containing oxygen and one or more volatile components by means of conductivities.

5. The composite material according to claim 1, characterized in that the composition of the crystalline mixed metal oxide is represented by SrFeCoo.s Od wherein d is a number representing the neutral charge of the compound, and wherein the composition has a powder X-ray diffraction pattern comprising substantially significant lines as described in Table I.

6. A hollow tubular module for membrane reactors, characterized in that the module comprises: (a-6) a dense ceramic membrane comprising a crystalline mixed metal oxide showing, at operating temperatures, electronic conductivity, ionic ionic conductivity, and ability to separate oxygen from a gaseous mixture containing oxygen and one or more components by means of conductivities; (b-6) an internal porous tube comprising an alloy of at least two metallic elements this tube shows mechanical stability at the operating temperature; (c-6) a first interface between the dense ceramic membrane and the inner porous tube having, through the interface, a composition gradient in at least one metal element; (d-6) an external porous tube comprising an alloy of at least two metallic elements this tube shows mechanical stability at the operating temperature; Y (e-6) a second interface between the dense ceramic membrane and the external porous tube which has, through the interface, a gradient of composition in at least one metallic element.

7. The hollow tubular module according to claim 6, characterized in that the dense ceramic membrane is made of the crystalline mixed metal oxide in a particulate form by compressing the particulate oxide against the internal and external porous tubes at temperatures near the melting point temperature of the desired ceramic, so that the composition gradients defining the first and second interfacial areas are obtained.

8. The hollow tubular module according to claim 7, characterized in that the alloy is a high temperature steel comprising at least nickel and chromium.

9. The hollow tubular module according to claim 8, characterized in that the composition of the crystalline mixed metal oxide is represented by SrFeCo0.5 Od wherein d is a number representing the neutral charge of the compound, and wherein the composition has a powder X-ray diffraction pattern comprising substantially significant lines as described in Table I.

10. A process for converting organic compounds into value-added products, characterized in that the composite comprises (a-10) providing a membrane reactor comprising a plurality of hollow tubular module according to claim 6; (b-10) contacting the outer porous tube of the hollow tubular module with a gaseous mixture containing oxygen having a relatively higher partial pressure of oxygen; (c-10) contacting the inner porous tube of the hollow tubular module with a gaseous composition having a relatively lower partial pressure of oxygen; Y; (d-10) allow oxygen to be transported through the dense ceramic membrane by means of its electronic conductivity and ionic oxygen conductivity thus separating the oxygen from the gas mixture containing oxygen having a partial pressure of oxygen relatively more high in the gaseous composition having a relatively lower partial pressure of oxygen.